1. Field of the Disclosure
The present disclosure relates to method and circuit for synchronizing input and output synchronizing signals, and more particularly to method and circuit for synchronizing input and output synchronizing signals, which can make fast synchronization of an output synchronizing signal to a change of a frequency of an input synchronizing signal, a backlight driver in a liquid crystal display device using the same, and a method for driving the backlight driver.
2. Discussion of the Related Art
In a flat display device for displaying an image by using a digital data, a liquid crystal display (LCD) device which uses liquid crystals, a plasma display panel PDP which uses discharge of inert gas, and an organic light emitting diode OLED which uses an organic light emitting diode are typical. Of the flat display devices, the liquid crystal display device has many fields of applications, such as TV sets, notebook computers, and cellular phones.
The liquid crystal display device displays a picture with a pixel matrix by utilizing electric and optical characteristics of the liquid crystals, which have anisotropy of refractive index and dielectric. Each pixel in the liquid crystal display device controls light transmissivity of a light transmitting through a polarizing plate by varying an orientation of the liquid crystals in response to a data signal, to produce a gradient. The liquid crystal display device is provided with a liquid crystal panel, which displays the picture with the pixel matrix, a driving circuit for driving the liquid crystal panel, a backlight unit for emitting a light to the liquid crystal panel, and a backlight driver for driving the backlight unit.
Recently, as the backlight unit, an LED backlight is being used, having a light emitting diode (Hereafter, LED) applied thereto, to have advantages of a fast tuning on speed, high brightness, and low power consumption compared to a related art lamps. The LED backlight emits a white light by using a white LED, or a combination of red/green/blue LEDs. And, the LED backlight has, not only an advantage of global dimming in which brightness of the backlight is controlled on the whole, but also an advantage of local dimming in which the brightness of the backlight is controlled location by location, i.e., block by block.
The backlight driver, which drives the LED backlight, generates a pulse width modulation PWM signal having a duty ratio matched to a dimming value received from an external system such as a TV set, or a timing controller. The backlight driver controls turn-on/turn-off time of the LED backlight according to the PWM signal for adjusting the brightness of the LED backlight.
In order to drive the LED backlight in synchronization with the liquid crystal panel, the backlight driver receives a vertical synchronizing signal from an external system for dividing frames of a video data. In order to deal with variation of a frequency of the vertical synchronizing signal received thus, the backlight driver calculates an input period of the vertical synchronizing signal at every frame for setting an output period, and generates an inner clock required for producing the duty of the PWM signal by using the output period of the vertical synchronizing signal.
However, in a case the input/output periods of the vertical synchronizing signals are calculated at every frame, if the frequency of the vertical synchronizing signal changes suddenly, the related art backlight driver fails to set the output period matched to the input period changed suddenly thus, consequently failing generation of the inner clock. According to this, the inner clock generation error causes the duty ratio to be outside of a desired range, resulting in a change of brightness of the LED backlight, causing a poor picture quality, such as flicker on a screen.